On MRI brain T2-weighted imaging, a hyperintense lesion is seen in the white matter of the right frontoparietal region with a 'soap-bubble' appearance and restricted diffusion. This pattern in an AIDS patient with CD4 count 50 cells/μL is most consistent with:
- A Toxoplasma encephalitis — typically ring-enhancing with surrounding edema
- B Primary CNS lymphoma — periventricular enhancing mass
- C Progressive Multifocal Leukoencephalopathy (PML) — JC virus demyelination ✓
- D HIV encephalopathy — diffuse symmetric white matter signal
Explanation
Progressive Multifocal Leukoencephalopathy (PML) caused by JC virus reactivation in severely immunocompromised patients (CD4 <100) appears as asymmetric multifocal white matter T2 hyperintensities with a 'soap bubble' or scalloped pattern, no significant mass effect, and no surrounding edema. Characteristically, PML lesions do not enhance (unless IRIS). Restricted diffusion at the advancing edge reflects active demyelination. Toxoplasma shows ring-enhancing lesions with significant edema and mass effect, often in the basal ganglia. Primary CNS lymphoma is periventricular, densely enhancing, and associated with restricted diffusion throughout.
Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.
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Written and medically reviewed by the StethoPrep medical team.